The invention relates to storing pictures into a memory and subsequently accessing the pictures, and more particularly, to efficiently storing and accessing pictures in multi-field video operations to reduce system cost.
There has been a rapid evolution from analog video technology to digital video technology because of the advantages that digital video has to offer. Digital video can be stored and distributed more cheaply than analog video because digital video can be stored on randomly accessible media such as magnetic disc drives (hard disks) and optical disc media known as compact discs (CDs). Once stored on a randomly accessible media, digital video may become interactive, allowing it to be used in games, catalogs, training, education, and other applications.
One of the newest products to be based on digital video technology is the digital video disc, sometimes called “digital versatile disc” or simply “DVD.” These discs are the size of an audio CD, yet hold up to 17 billion bytes of data, 26 times the data on an audio CD. DVD storage capacity (17 Gbyte) is much higher than CD-ROM (600 Mbyte) and a DVD can deliver the data at a higher rate than CD-ROM. Therefore, DVD technology represents a tremendous improvement in video and audio quality over traditional systems such as televisions, VCRs and CD-ROM.
However, a major problem in utilizing DVD and other digital video technology to display motion pictures is that the sources of motion pictures come at different frame speeds. For example, standard film is shot at a rate of 24 Hz while a television broadcast using the National Television System Committee (NTSC) standard updates motion at 60 Hz. Converting the motion picture into digital video through a process called scan-rate conversion often produces a noticeable reduction in resolution as well as distortions known as motion artifacts.
Deinterlacing processes are used for video scan-rate converting, and an exemplary application of deinterlacing is used in TV systems as a reverse process for interlacing. To transmit a video signal in an “interlaced” format (or read the signal in interlaced format from memory), One kind of methods is that the odd field of each frame is transmitted (or read) before the even field of the frame. In other words, all the odd-numbered active video lines of the frame are transmitted (or read) before any of the even-numbered active video lines are transmitted (or read). When a video signal in such interlaced format is displayed on a video monitor, all of the odd lines appear on the monitor before any of the even lines appears on the monitor.
To transmit (or read) a video signal in a “progressive” format, the active video lines of a frame are transmitted (read) in consecutive order (line “1,” followed by line “2,” followed by line “3,” and so on). When a progressive-format signal is displayed on a video monitor, the lines appear on the screen in this same consecutive order (with an odd line appearing immediately before each even line).
Therefore, the above mentioned deinterlacing is a very important image format transformation process. Generally speaking, high quality deinterlacing functions always require the use of a large amount of memory and high memory bandwidth. Because, in the deinterlacing process, it is possibly required to store a large amount of field picture data, cost effective memory components such as dynamic random access memories (DRAM) are often utilized. Note, either off-chip DRAMs or embedded DRAMs are both commonly employed for deinterlacing. Furthermore, because access of large sized DRAMs may result in memory system congestion, system designers are typically required to use higher speed DRAM devices, or to use a system with other memory modules with larger amounts of local buffering support to pre-fetch or temporarily store data of the memory to prevent temporary loss of data access.
FIG. 1 shows how four fields 101, 102, 103, 104 are utilized to complete deinterlacing according to a typical deinterlacing process. The deinterlacing process needs to use data for at least one field picture to produce a frame picture. For example, in FIG. 1, data of four field pictures 101, 102, 103, 104 is required to be passed to a deinterlacing unit for further processing.
FIG. 2 shows how the data of the four fields 101, 102, 103, 104 of FIG. 1 are typically stored in a memory 200. As mentioned, traditionally speaking, the deinterlacing process requires taking a plurality of field pictures and providing a linear mapping method to store these field pictures in a memory such as a DRAM. A raster scan method can be utilized to read the data from the memory for transfer into a deinterlacing unit for further processing.
A typical deinterlacing unit includes a plurality of local line buffers to store current pixel data that is required to be used during the deinterlacing process. Different field data is then alternatively transferred into the local line buffers of the deinterlacing unit from the memory 200 throughout the deinterlacing process. For example, a portion of the data of a first field 101 will first be transferred to a local line buffer, then data of a second field 102, third field 103, and fourth filed 104 is sequentially transferred to the local line buffers. Afterwards, new data from the first field 101 is transferred into the line buffer and the process repeats. This type of alternating access of data of different fields while moving the data into the local line buffers means that it is very easy to encounter DRAM page misses while accessing the DRAM memory 200. As the probability of page misses increases, the efficiency of DRAM bandwidth usage is reduced. This results in the efficiency of the entire system also being degraded, and of the actual time required by the deinterlacing process to complete to be further extended. For example, experiments show that losses due to one time DDR DRAM page miss can reach 10%-75%, which mainly depends on data bus widths and burst lengths. In DDR2 DRAM, one page miss can further reach to 33.3%-250%.